“…(2) Sample digestion [9]: For grain and bean samples, weigh 0.25g (accurate to 0.001g) into a polytetrafluoroethylene (PTFE) digestion tank, add 6mL nitric acid (MOS grade), cover and place for 1h, and then put it into a graphite digester for digestion; For vegetable samples, weigh 0.1g (accurate to 0.001g) of solid samples into a PTFE digestion tank, add 6mL of nitric acid (MOS grade) and 1.5mL of hydrofluoric acid (EP grade), pre-digest at 100 ℃ for one hour on the graphite digester, and then cover to continue digestion. The digestion temperature procedure is as follows: 120 ℃ digestion for 0.5h, 150 ℃ digestion for 10min, 180 ℃ digestion for 0.5h, after digestion to clear, set the temperature to 140 ℃, drive the acid to about 1 mL of colorless or light yellow clear liquid, stop, transfer the digestion solution to a 25ml centrifuge tube (PP material), wash the digestion tank with deionized water 2-3 times, and the washed liquid is also transferred into the centrifuge tube, and finally use deionized water to volume, use 0.45 μm PTFE needle filter is filtered, and then tested on the machine.…”